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Results 401 - 450 of 823
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Munger K A - - 1994
We examined the renal effects of a specific adenosine A1-receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 micrograms.kg-1.min-1 iv). Since adenosine is a potent inhibitor of renin release, additional experiments were performed with an angiotensin AT1-receptor antagonist (losartan, 10 mg/kg i.v.). DP CPX alone induced a significant (P < 0.05) decrease in afferent ...
Bolling S F - - 1994
During induced ischemia for cardiac surgery, nucleotides are degraded while being used to maintain myocyte integrity. The resulting nucleosides washout upon reperfusion, limiting nucleotide resynthesis resulting in poor postischemic cardiac function. We studied if the mechanism of the beneficial effect of adenosine, a nucleotide precursor, which is known to improve ...
Portman M A - - 1994
The purpose of this study was to measure myocardial buffering capacity and adenosine triphosphate utilization rates in the newborn animal in vivo during hypothermic circulatory arrest and recovery. METHODS: These studies were performed with 31P magnetic resonance spectroscopic techniques, which supplied a 12- to 16-second time resolution, to monitor intracellular ...
Wannenburg T - - 1994
We studied the effects of adenosine on oxygen consumption and contractile state in 17 isolated, crystalloid-perfused, isovolumically contracting rat heart preparations at constant coronary flow. In 10 experiments we determined adenosine-contractile state dose-response relationships in three groups of hearts using two different perfusates and in the presence and absence of ...
Cabell F - - 1994
The aim of the present study was to investigate the contribution of large-conductance calcium-activated potassium (large-conductance KCa) channels to adenosine (Ado)- and nitroprusside-mediated relaxation in small coronary arteries. Canine subepicardial arteries (170 +/- 23 microns at 120 mmHg) were studied as in vitro pressurized vessels. Pressure-diameter experiments showed myogenic tone ...
Dawid-Milner M S - - 1994
In pentobarbitone anaesthetized and paralysed cats the effects of the A1 adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) have been observed on the pressor response to stimulation of the hypothalamic defence area (HDA) and on the effects of baroreceptor and chemoreceptor reflex activation on arterial blood pressure. The administration of DPCPX decreased the ...
Komaru T - - 1994
Previous studies in which an isolated heart or in situ constant pressure preparation was used suggested a minimal role for adenosine in autoregulatory control of coronary circulation. These results, however, are controversial, and the role of adenosine in autoregulation of flow in heart is uncertain. To test the hypothesis that ...
Schjøtt J - - 1994
We examined whether pretreatment with lidocaine could influence the cardiac kinetics of adenosine and thereby strengthen the physiologic responses of the nucleoside, either exogenously administered or endogenously produced. Isolated rat hearts perfused with lidocaine, 0.05 microM to 500 microM, were subjected to 6 min. of adenosine infusion followed by 30 ...
Thomas T - - 1994
In two groups of Saffan-anaesthetized, spontaneously breathing rats we have attempted to identify the peripheral influences of adenosine in mediating the responses evoked by hypoxia by using an adenosine receptor antagonist, 8-sulphophenyltheophylline (8-SPT, 20 mg kg-1 i.v., Group 1) and adenosine deaminase (ADA, 500 units in 0.04 ml infused into ...
Allard M F - - 1994
The contribution of glycolysis and oxidative metabolism to ATP production was determined in isolated working hypertrophied hearts perfused with Krebs-Henseleit buffer containing 3% albumin, 0.4 mM palmitate, 0.5 mM lactate, and 11 mM glucose. Glycolysis and glucose oxidation were directly measured by perfusing hearts with [5-3H/U-14C]glucose and by measuring 3H2O ...
Clarke K - - 1994
To quantify metabolite and cation concentrations using NMR spectroscopy, the volumes of intracellular and extracellular spaces must be known. We describe a simple 31P NMR spectroscopic method that employs dimethyl methylphosphonate (DMMP) as a marker of total water space and phenylphosphonate (PPA) as a marker of extracellular space to determine ...
Sellke F W - - 1994
Crystalloid cardioplegia may cause coronary microvascular endothelial dysfunction during cardiopulmonary bypass. The perioperative administration of either adenosine or AICA-riboside (acadesine, 5-aminoimidazole-4-carboxamide-1-ribofuranoside) has been associated with improved myocardial functional preservation and improved coronary blood flow after ischemic arrest. To examine if this enhanced recovery of myocardial function and perfusion may be ...
Offstad J - - 1994
OBJECTIVE: ATP gated potassium (KATP) channels and adenosine are of crucial importance in coronary blood flow regulation and activation of KATP channels and adenosine receptor stimulation protect against infarction and development of stunning. The aim of this study was to test the hypothesis that opening of KATP channels and adenosine ...
Shinzato T - - 1994
First, this investigation showed that plasma levels of inosine, hypoxanthine, and xanthine, which are metabolites of adenosine, rose sharply when blood pressure dropped suddenly along with symptoms during a hemodialysis session (sudden hypotension), but not when it decreased gradually with eventual symptoms (gradual hypotension). Because adenosine has an action to ...
Vials A J - - 1994
The Langendorff heart preparation was used to investigate the mechanism of action of vasodilatation evoked by ATP and its analogues in guinea pig coronary vasculature. The relative order of potency of ATP and its analogues in causing a reduction in perfusion pressure was 2-methylthioATP (2-meSATP) > ATP > beta, gamma-methyleneATP ...
Bache R J - - 1994
Spatially localized nuclear magnetic resonance (NMR) spectroscopy was used to examine the effect of tachycardia and inotropic stimulation on myocardial ATP, creatine phosphate (CrP), and inorganic phosphate (Pi) in animals with left ventricular hypertrophy (LVH). Studies were performed in eight normal dogs and seven dogs with moderate LVH produced by ...
Yao Z - - 1994
BACKGROUND: Adenosine has been proposed to be an important mediator of ischemic preconditioning. Intracoronary administration of adenosine has recently been shown to mimic the effects of preconditioning in isolated rabbit hearts. However, it is not known whether this agent can duplicate the effects of preconditioning in vivo or in other ...
Wilson A N - - 1994
1. The role of adenosine in the control of coronary vessel tone was studied using two guinea-pig hearts in series. Vasodilatory mediator(s) released by the donor heart were assayed by the recipient heart. 2. Adenosine deaminase reduced the activity of vasodilatory mediator(s) released by histamine and isoprenaline by 58.0 +/- ...
Koglin J - - 1994
OBJECTIVES: The purpose of this study was to investigate the antiadrenergic effects of adenosine and carbachol on beta-adrenoceptor-stimulated human ventricular contractility in vivo. In addition, the antiadrenergic effects of adenosine and carbachol were compared in vitro. BACKGROUND: Adenosine is reported to exhibit an antiadrenergic negative inotropic response in the beta-adrenergic-stimulated ...
Vander Elst L - - 1994
The biochemical and mechanical effects of a new calcium ion channel antagonist, fantofarone ((2-isopropyl-1-((4-(3-(N-methyl-N-(3,4-dimethoxy-beta-phenethyl)-amino) propyloxy)benzenesulfonyl))-indolizine), on isovolumic perfused rat heart have been assessed by using 31P nuclear magnetic resonance (NMR) spectroscopy together with simultaneous monitoring of myocardial mechanical function. Cytosolic pH and phosphocreatine, adenosine triphosphate and inorganic phosphate contents were ...
Elliott A C - - 1994
1. The metabolic consequences of an increase in the frequency of stimulation were examined in isolated ferret hearts. Intracellular pH (pHi) and the intracellular concentrations of phosphocreatine ([PCr]i), inorganic phosphate ([Pi]i) and ATP were measured by 31P nuclear magnetic resonance (NMR) spectroscopy. 2. Increasing the stimulus rate from 0.1-0.7 to ...
Jacobson A F - - 1994
Although caffeine attenuates the vasodilatation produced by dipyridamole and adenosine, and is therefore contraindicated when these agents are used for myocardial perfusion scintigraphy, caffeine levels in clinical patients undergoing standard imaging protocols have not been studied. Eight-six patients undergoing clinically indicated intravenous dipyridamole (n = 75) or adenosine (n = ...
Ikeda Y - - 1994
This study was designed to examine the effects of an adenylate cyclase activator, NKH477, on epicardial and endocardial contraction and coronary blood flow (CoF) in the presence or absence of ischemia and to compare it to those of adenosine. We measured coronary pressures (CoP), coronary blood flow, epicardial and endocardial ...
Wilson D F - - 1994
Mitochondrial oxidative phosphorylation in vivo is dependent on the degree of reduction of the intramitochondrial reducing power ([NADH]/[NAD+], cytoplasmic energy state ([ATP]/[ADP][Pi]) and intracellular oxygen pressure. Each parameter is independently regulated, and increased reducing power by activating the mitochondrial dehydrogenases allows higher energy state at a given rate of ATP ...
Ernst M - - 1994
The effects on brain metabolism of the intravenous (i.v.) administration of dextroamphetamine was assessed by positron emission tomography (PET) with [18F]-fluorodeoxyglucose (18-FDG) in 8 adults with attention-deficit hyperactivity disorder (ADHD). During the 3-hour 18-FDG PET session, each adult underwent the initial scan following i.v. infusion of placebo and a second ...
Hale S L - - 1993
OBJECTIVE: A preconditioning mimetic agent could be useful therapy for cardiac ischaemic events; stimulation of adenosine receptors has been proposed as a preconditioning mediator. The ability of adenosine-receptor activation to mimic ischaemic preconditioning was tested in an in vivo rabbit model. METHODS: Adenosine (15 mg, a maximally tolerated dose, n ...
Wittenberg B A - - 1993
By sequestering intracellular myoglobin of cardiac muscle cells in the nonfunctioning carboxymyoglobin form, carbon monoxide blocks myoglobin-facilitated diffusion of oxygen, as well as myoglobin-mediated oxidative phosphorylation. Here, we explore the hypothesis that the carbon monoxide blockade of myoglobin function may be responsible at the cellular level for a component of ...
Kitai T - - 1993
The energy metabolism of the heart and the liver was assessed in brain-dead dogs by 31P nuclear magnetic resonance spectroscopy. The mean blood pressure and pulse rate changed respectively from 136.1 +/- 9.3 mm Hg (mean +/- SEM) and 126.7 +/- 4.4/min in the control period, to 212.9 +/- 15.8 ...
Hak J B - - 1993
We investigated whether a glycolytic burst contributes to the initial adaptation of ATP synthesis to increased cardiac metabolic demand. Six isolated rabbit hearts were perfused with glucose-containing Tyrode solution at 28 degrees C. In venous and arterial samples the lactate concentration was determined with a sensitive enzymatic cycling method. After ...
Martin S E - - 1993
OBJECTIVES: Whether intracoronary papaverine or adenosine leads to reductions in regional left ventricular function was tested. METHODS: Fifteen anaesthetised dogs were prepared to record aortic pressure, left ventricular pressure dP/dt, electrocardiogram, regional ventricular shortening, and phasic and mean left circumflex coronary blood flow, and to give intracoronary boluses of papaverine ...
Heller G V - - 1993
This study was designed to evaluate the effects of intravenous theophylline given before intravenous adenosine for thallium-201 imaging. Sixteen patients with known reversible thallium-201 defects were randomized to a double-blind crossover study of a 45-minute infusion of placebo or theophylline (given as the ethylenediamine salt, aminophylline, mean concentration 16.1 mg/L) ...
Zanzinger J - - 1993
We investigated the effects of inhibition of both nitric oxide (NO) synthesis and angiotensin converting enzyme (ACE) on agonist-induced relaxations in the coronary system. Chronically instrumented conscious dogs (n = 4) were prepared for the measurement of coronary blood flow (CBF), coronary diameter of the left circumflex artery (LCX), mean ...
Altura B M - - 1993
Hemodynamic and 31P-NMR spectroscopic studies were performed on intact, perfused working rat hearts exposed to low (0.3 mM) extracellular Mg([Mg2+]o). Low [Mg2+]o perfusion resulted in rapid and significant falls in cardiac output, coronary flow, stroke volume, developed pressure and the rate-pressure product. Concomitant with this O2 consumption decreased and lactate ...
Kupriyanov V V - - 1993
The response of cytosolic phosphates ([ATP], [PCr], [Pi] and [ADP]) in rat hearts retrogradely perfused with different oxidizable substrates to increased workload induced by elevated coronary flow (CF) or by addition of inotropic agents has been investigated. Hearts were perfused with glucose (11 mM), pyruvate (5 mM), lactate (3 mM) ...
Murphy E - - 1993
Preconditioning with brief intermittent periods of ischemia has been shown to lessen the detrimental effects of a subsequent sustained (30-60 min) period of ischemia. Because adenosine has been suggested to be the mediator of preconditioning, we were interested in investigating whether adenosine antagonists would block the effect of preconditioning on ...
Webb R L - - 1993
Three highly A2a-selective adenosine agonists were examined for their effects on blood pressure during chronic administration in conscious spontaneously hypertensive rats. Sodium 4-[2-[[6-amino-9-(N-ethyl-beta-D-ribofuranuronamidosyl)-9H-purin-2 -yl] amino]ethyl]benzenepropionate (CGS 21680C) 2-[(2-cyclohexyl-ethyl)amino]adenosine (CGS 22492) and 2-[[2-(1-cyclohexen-1-yl)ethyl]amino]adenosine (CGS 22989) were administered at a rate of 0.25 and 0.5 micrograms/kg/min i.v. for 2 weeks using osmotic ...
Kito K - - 1993
Hepatic blood flow (HBF) and energy metabolism during moderate hypotension induced by prostaglandin E1 (PGE1) and nicardipine were studied by in vivo magnetic resonance spectroscopy. HBF was determined by the deuterated water clearance method by using deuterium magnetic resonance spectroscopy, and energy metabolism was estimated from the changes in the ...
Read M A - - 1993
1. The vasoactive effects of adenosine triphosphate (ATP), adenosine and other purines in the foetal circulation of the human placenta were examined. Single lobules of the placenta were bilaterally perfused in vitro with Krebs buffer (maternal and foetal sides 5 ml min-1 each, 95% O2:5% CO2, 37 degrees C). Changes ...
Van Wylen D G - - 1993
OBJECTIVE: Adenosine is a well known vasodilator believed to contribute to metabolic adjustments of the coronary circulation. The purpose of this study was to assess changes in interstitial fluid adenosine, adenosine metabolites, and lactate during prolonged regional, non-ischaemic myocardial hypoxia. METHODS: To induce regional hypoxia, the left anterior descending coronary ...
Gidday J M - - 1993
PURPOSE: To determine if the purine vasodilator adenosine participates in mediating autoregulatory dilations of the retinal microcirculation in vivo. METHODS: The retinal microcirculation of isoflurane-anesthetized newborn pigs was observed by videomicroscopy (x310). Systemic hypoxia (PaO2 = 24 +/- 1 mm Hg; n = 8) or hemorrhagic hypotension (MABP = 41 ...
Smolenski R T - - 1993
A reversed phase high performance liquid chromatographic technique is presented allowing purine catabolite determination in a whole blood extract without a prior purification step. The method was applied to determine the timing and the profile of myocardial nucleotide catabolite release during reperfusion of the transplanted human heart. Samples of arterial ...
Heinle S - - 1993
Echocardiography and thallium-201 imaging with coronary vasodilators such as dipyridamole have been shown to be useful in detecting the presence and prognostic significance of coronary artery disease. Adenosine, a potent and direct coronary vasodilator, has a shorter physiologic half-life than dipyridamole, which exerts its effect by blocking the cellular uptake ...
Mason B A - - 1993
OBJECTIVE: We determined the cardiorespiratory effects of maternal adenosine administration on the ewe and fetus. STUDY DESIGN: Adenosine was infused intravenously to five pregnant ewes as graded (25 to 400 micrograms/min per kilogram) and constant (200 micrograms/min per kilogram) infusions and as a single injection (200 micrograms/kg). Heart rate, arterial ...
Hak J B - - 1993
The purpose of this study was to investigate the effect of acidosis on the mean response time of mitochondrial oxygen consumption to steps in heart rate and in left ventricular balloon volume. The mean response time may be viewed as the average delay between a change in adenosine triphosphate (ATP) ...
Nichols D G - - 1993
We tested whether fatigue of the piglet diaphragm is associated with inadequate oxidative metabolism as measured by magnetic resonance spectroscopy (MRS). An MRS measured ratio of inorganic phosphate to phosphocreatine (Pi/PCr) > or = 1 was taken as evidence of inadequate oxidative metabolism. Piglets (n = 10) underwent phrenic nerve ...
Shen Y T - - 1993
The systemic, coronary and regional vascular responses to the K+ATP channel opener lemakalim were compared to other potent vasodilators (i.e., nifedipine, adenosine, nitroglycerin and acetylcholine). Experiments were performed in 12 conscious dogs 2 to 4 weeks after implantation of aortic catheters and flow probes on the ascending aorta, left circumflex ...
Achike F I - - 1993
1. The addition of adenosine, CO2 and lactate to the venous blood draining an isolated constant-flow perfused gracilis muscle was studied in anaesthetized and artificially ventilated dogs during twitch and tetanic contractions. 2. Venous adenosine concentration increased from 154 +/- 33 nM (mean +/- S.E.M.) to 279 +/- 121 or ...
Leone R J RJ - - 1993
Twenty-six beagles of either sex, weighing 10.4 +/- 0.3 kg, were used to investigate the role of adenosine in the genesis of ventricular arrhythmias during systemic hypoxia. After instrumentation dogs were randomly assigned to one of four treatment groups: 14 dogs were pretreated before hypoxia with adenosine deaminase (n = ...
Fenton R A - - 1993
Endogenous interstitial adenosine may protect the hypoxic heart by attenuating beta-adrenergic-induced contractile and metabolic responses, thereby reducing energy utilization. Constant-flow perfused rat hearts were used to study: 1) the effect of hypoxia on isoproterenol (ISO)-induced increase in interstitial adenosine, as estimated with epicardial surface transudates, and 2) the role of ...
Zäll S - - 1993
In the early postoperative period after coronary artery bypass surgery, arterial hypertension commonly occurs which requires intravenous vasodilator therapy. Purine adenosine is a potent vasodilator and when exogenously administered it decreases systemic arterial blood pressure effectively. We evaluated the effects of adenosine on central hemodynamics and renal function when used ...
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